format: add --api-prefix CLI option (#3108)
format: add --api-prefix CLI option (#3108)

Needed for checking format when embedded in a parent project.

Signed-off-by: Matt Klein <684e4e870ef5a243d6d0345280f09d95db603639@lyft.com>
istio/envoy,dnoe/envoy,lyft/envoy,sebrandon1/envoy,envoyproxy/envoy,lyft/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy-wasm,eklitzke/envoy,envoyproxy/envoy,jrajahalme/envoy,envoyproxy/envoy,eklitzke/envoy,istio/envoy,envoyproxy/envoy,dnoe/envoy,istio/envoy,lyft/envoy,istio/envoy,sebrandon1/envoy,jrajahalme/envoy,envoyproxy/envoy,envoyproxy/envoy,lizan/envoy,lizan/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy-wasm,sebrandon1/envoy,jrajahalme/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy-wasm,jrajahalme/envoy,envoyproxy/envoy-wasm,lizan/envoy,eklitzke/envoy,envoyproxy/envoy-wasm,dnoe/envoy,sebrandon1/envoy,envoyproxy/envoy,dnoe/envoy,jrajahalme/envoy,istio/envoy,lyft/envoy,jrajahalme/envoy,lyft/envoy,envoyproxy/envoy,dnoe/envoy,istio/envoy,eklitzke/envoy,eklitzke/envoy,lizan/envoy,lizan/envoy,lyft/envoy,sebrandon1/envoy,istio/envoy,eklitzke/envoy,lizan/envoy